I support a lot of my clients with English writing projects, helping them to improve grammar, vocabulary content and general style. I enjoy that kind of work and am sure I can help you improve.
My proposal would be (the way I work with my other clients) that you send a piece of writing (1-2 pages). I would then highlight sections which need correction and add a comment e.g. grammar, vocab, style, word order etc. This would then be returned to you and you should then try to make improvements based on my comments. This is a good way for you to improve rather than me simply correcting/changing your work immediately. I would then look at the second version and add detailed comments and improvements where necessary.